Engine air-to-fuel ratio control system

Abstract

A system for controlling an air-to-fuel ratio of a gas mixture supplied to a vehicle engine to a correct valve is disclosed. In response to an output signal from a discriminator circuit which receives as inputs thereto a signal from an air-to-fuel ratio detector mounted in an exhaust pipe and simultaneously in response to a signal from an aperture detector which detects the aperture of a control valve mounted in an adjusting air path provided parallel to a carburetor, a pulse motor for adjusting the aperture of the control valve provided in said air path is driven to obtain a correct air-to-fuel ratio.

What we claim is: 
     
       1. An air-to-fuel ratio control system for an internal combustion engine comprising: a carburetor connected to an intake pipe of an internal combustion engine for supplying air-fuel mixture to said engine;   said carburetor including:   a main passage provided with a throttle valve for controlling the amount of the air-fuel mixture, and   a bypass passage provided with a bypass valve for compensating air-to-fuel ratio of the air-fuel mixture by controlling the amount of air flowing therethrough;   an air-to-fuel ratio detecting means mounted in an exhaust pipe of said engine for detecting the air-to-fuel ratio of the mixture supplied to said engine;   valve position detecting means for detecting a valve position of said bypass valve;   a bypass valve control circuit connected to said air-to-fuel ratio detecting means and said valve position detecting means in which a bypass valve control signal is produced in accordance with the respective outputs of said air-to-fuel ratio detecting means and said valve position detecting means; and   driving means coupled to and driving said bypass valve in response to said bypass valve control signal so that the driving speed of said valve increases as the valve opening increases .   
     
     
       2. An air-to-fuel ratio control system as set forth in claim 1, wherein said valve position detecting means comprises; a potentiometer coupled to said bypass valve for producing an output voltage corresponding to the opening position of said bypass valve, and   said bypass valve control circuit comprises; a pulse generator for generating pulse signals whose frequency corresponds to said output voltage from said valve position detecting means; and   a switching circuit connected to said air-to-fuel ratio detecting means and said pulse generator in which the bypass valve control signal having a frequency corresponding to the frequency of said pulse signals is produced whereby said driving means drives said bypass valve with a control speed corresponding to the frequency of said bypass valve control signal.   
     
     
       3. An air-to-fuel ratio control system as set forth in claim 1, wherein said valve position detecting means comprises; a fully-closed position detecting switch coupled to said bypass valve for producing an output signal when said bypass valve is positioned at its fully-closed position, and said bypass valve control circuit comprises;   a pulse generator for generating pulse signals, the frequency of said pulse signals being changed in proportion to an input voltage supplied to the input terminal of said pulse generator;   a counter circuit connected to said fully-closed position detecting switch in which said pulse signals is counted in accordance with the output of said air-to-fuel ratio detecting means, said counter circuit being reset for counting by said output signal from said fully-closed position detecting switch;   
     
     
       a D-A converter connected to said counter circuit for producing an output voltage to be supplied to said input terminal of said pulse generator, the value thereof being in proportion to the number of pulses counted by said counter circuit; a switching circuit, connected to said air-to-fuel ratio detecting means and said pulse generator in which the bypass valve control signal having the frequency corresponding to the frequency of said pulse signals is produced whereby said driving means drives said bypass valve with a control speed corresponding to the frequency of said bypass control signal.   
     
     
       4. An air-to-fuel ratio control system as set forth in claim 1 wherein said byapss valve comprises a butterfly valve, and wherein said bypass passage is provided with a channel formed at a portion thereof facing to a tip end of said butterfly valve. 
     
     
       5. An air-to-fuel ratio control system as set forth in claim 1 wherein said bypass valve control circuit comprises discriminator circuit means connected to said air-to fuel detecting means for producing an output signal depending on whether the output of said air-to-fuel ratio detecting means is higher or lower than a predetermined reference value, pulse generator means connected to said valve position detecting means for producing a pulse signal having a frequency which is variable in accordance with the variation of said valve position detecting means, reversible command circuit means connected to both said discriminator circuit means and said pulse generator means for producing forward and reverse rotation command signals in accordance with the output signal of said pulse generator means, reversible shift register means connected to said reversible command circuit means for producing a plurality of output signals which are sequentially shifted in accordance with said forward and reverse rotation command signals, switching circuit means connected to said reversible shift register means for sequentially energizing said drive means. 
     
     
       6. A method for controlling an air-to-fuel ratio of air-fuel mixture to be supplied to an internal combustion engine comprising the steps of. applying air-fuel mixture to an internal combustion engine through a main passage;   controlling the relative proportion of air-to-fuel in the air-fuel mixture being admitted through said main passage in accordance with a commanded position of a throttle valve provided in said main passage;   measuring oxygen content of the exhaust gases from said engine;   applying auxiliary air to said engine through a bypass passage;   controlling the amount of air being admitted through said bypass passage in accordance with the measured oxygen content of the exhaust gases by driving a bypass valve provided in said bypass passage;   detecting an opening position of said bypass valve; and   changing a control speed for driving said bypass valve in accordance with the detected opening position of said bypass valve.